I have some mergwen stories how do I go about downloading them onto here?
It depends :)
Stories you've written yourself
Depending on the length, you may wish to upload them to an external fanfiction hosting site like archiveofourown or livejournal. If so, upload the story there, and then create a post linking to the story on tumblr. Tag your story with "merwen" and I will reblog it :)
If your story is short, I recommend just uploading it straight to tumblr in a text post. Put the title of your story in the title, write the summary, then create a "read-more" cut and post the content of your story beneath this. Tag your story with "merwen" and I will reblog it :)
Other people's stories
Create a post linking to the story on tumblr, tag it with merwen, and I will reblog it :) Alternatively, you can just send me the link in the ask or submit box and I will make a post for it (remembering to send the link in the following way, as tumblr does not allow you to send links in asks;
www(.)yourlinkhere(.)com/whatever